According to the latest research, the safest plastics for use with food are high-density polyethylene, low-density polyethylene, and polypropylene. Virtually all sous vide bags are made from these plastics, as are most brand-name food storage bags and plastic wraps such as Saran wrap. Polyethylene is widely used in containers for biology and chemistry labs, and it has been studied extensively. It is safe.

Less expensive, bulk plastic wraps sold to the catering trade are not as safe, however. These products are commonly made from polyvinyl chloride (PVC), which can contain harmful plasticizers that have been shown to leach into fatty foods such as cheese, meat, and fish. Legitimate concerns exist about food exposed to these plastics at high temperatures. Polyethylene-based plastic wraps are available at only slightly higher costs and do not raise such concerns. An easy way to spot the difference is to check that your cling wraps or plastic bags are rated microwave-safe. Bags and wraps made form polyethylene are generally microwave-safe, whereas those that contain polyvinyl chloride plastics generally are not.

Many professional kitchens use clear, rigid, plastic storage containers that are made from polycarbonate. While they are currently approved for food use, these plastics also may be a cause for concern because they contain bisphenol A (BPA), a chemical that can disrupt hormone activity and leach into foods and beverages. Cracks and crazing due to wear and tear increase the rate at which BPA leaches out of polycarbonates.

The bottom line is that bags made expressly for cooking sous vide are perfectly safeas are oven bags, popular brands of zip-top bags, and stretchy plastics such as Saran wrap. If you remain hesitant to try cooking sous vide due to concerns over plastic, you can always use canning jars instead, but beware that cooking times will be longer.

This blog post has a solid summary of the issue, and a recent study found many BPA free bags still leach chemicals with estrogenic activity (EA). I won’t dive into why this is problematic but was curious if you have seen this study.

@Justin –
The paper raises some important questions. With regards to sous vide cooking, while the study did find that a significant percentage of HDPE products contained detectable levels of EA, the stress (>100 C autoclave, repeated microwave exposure, etc) exposed to these products were very different from the type of stress occurring during sous-vide cooking. This study shows that we are learning more and more about the chemicals that surround us, though it does not answer questions such as the health effects of EA on humans, and if there are indeed negative effects, the minimum dosage for detection. For now, as nom nom paleo concludes as well, bags made specifically for sous vide are your best bet.

According to the Pacific Northwest Pollution Prevention Resource Center, no studies were found in the literature evaluating migration of chemical additives from plastics in simulated Sous Vide conditions. And manufacturers have been unwilling to disclose the full formulations and additives. Source: http://goo.gl/yZRrw7

So, I am opinion, whether “bags made expressly for cooking sous vide are perfectly safe” is still an open question.

I use a sheet of plastic wrap filled with flour and twisted closed to form a bag when blind baking tart shells. I get much better results as compared to using pie weights. My assumption is that with the dough being ~20-25% by weight butter, and butter being ~16% water, that the steam rising off from the tart shell as it bakes, keeps the plastic wrap from ever heating beyond 100 C / 212 F. Especially since you only blind bake for ~15 minutes.